Defective motors are repaired by removing the conductor coils from the magnetic iron core and rewinding the core. The coils are, of course, insulated, and are usually held in place by varnish impregnant, wedges, and end blocks. This material, which consists largely of thermoset resins, must be removed or destroyed in order to remove the coils. The usual practice is to burn out the thermoset resins. Burning, however, produces pollutants, uses energy, and leaves a char which is difficult to remove.
An alternative procedure is to immerse the motor in a stripper composition. Commercial strippers, however, swell the resin without destroying it, and a swelled resin may be no easier to remove than an unswelled resin.